They should be able to accommodate you all in the MDR. However, you should visit one of the MDRs and speak with the maître d' and they might be able to have a table ready for you at the time you'd like to eat. Otherwise your group could have a lengthy wait for enough table space to open up.
I've never cruise with a group that large (just 6), so I'm not the best person to answer, just speaking on what I've heard that they might do.